Designs of efficient plasmonic probe for near-field scanning optical microscopy
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We present a novel concept to design apertureless plasmonic probes for near-field scanning optical microscopy (NSOM) with enhanced optical power throughput and near-field confinement. Specifically, we combine unidirectional surface plasmon polariton (SPP) generation along the tip lateral walls with nanofocusing of SPPs through adiabatic propagation towards an apertureless tip. Three probe designs are introduced with different light coupling mechanisms. Optimal design parameters are obtained with 2D analysis and realistic probe geometries with patterned plasmonic surfaces are proposed using the optimized designs. The electromagnetic properties of the designed probes are characterized in the near-field and compared to those of a conventional single-aperture probe with same pyramidal shape. The optimized probes feature enhanced light localization in near-field of tip apex and improved optical throughput. Our ideas effectively combine the resolution of apertureless probes with throughput levels much larger than those available even in aperture-based devices.